Measured GFR at 60 mL/min/1.73 m2 Carries a Clear Outcome Penalty
A measured glomerular filtration rate of 60 mL/min/1.73 m2 was associated with materially worse outcomes than a value of 90 mL/min/1.73 m2 in a large Swedish cohort, reinforcing the clinical logic behind the current chronic kidney disease threshold. In this retrospective study of 6,174 adults from Stockholm, lower kidney function tracked with higher rates of all-cause mortality and kidney failure with replacement therapy, and the risk gradient was not subtle.
During a median follow-up of 5.9 years, 1,977 participants died and 426 progressed to kidney failure requiring replacement therapy. Median age was 59 years, and the cohort was predominantly male, with 3,686 men and 2,488 women. These were not abstract modeling outputs detached from bedside medicine; they were outcome events occurring in a real clinical population whose kidney function had been assessed with iohexol plasma clearance, a direct measure of filtration rather than an estimate derived from biomarkers alone.
At baseline, an mGFR of 60 mL/min/1.73 m2 corresponded to 27.6 deaths per 1,000 person-years versus 22.4 at 90 mL/min/1.73 m2. The adjusted hazard ratio for death was 1.21, with a 95% confidence interval of 1.14 to 1.28. For kidney failure with replacement therapy, the contrast was even sharper: 1.2 versus 0.4 events per 1,000 person-years, with an adjusted hazard ratio of 2.85 and a 95% confidence interval of 2.06 to 3.94. A drop in filtration from 90 to 60 did not merely mark a laboratory shift; it mapped onto a substantial increase in clinically meaningful events.
Biologically, the finding fits the long-recognized role of reduced filtration as a proxy for systemic vascular and renal injury. Lower GFR often reflects chronic nephron loss, microvascular disease, and cumulative exposure to metabolic and hemodynamic stressors that raise mortality risk long before dialysis or transplant becomes necessary. The mortality signal in this study suggests that the threshold used to define chronic kidney disease is not arbitrary. It captures a level of kidney impairment at which downstream cardiovascular and renal consequences become measurably more common.
Creatinine-Cystatin C Estimates Matched Measured Risk Most Closely
The comparison between measured and estimated kidney function is where the study becomes especially useful for daily practice. Investigators evaluated three common estimating strategies: creatinine-based eGFR, cystatin C-based eGFR, and the combined creatinine-cystatin C equation. For mortality, the combined equation tracked the measured GFR association most closely. At 60 mL/min/1.73 m2, the ratio of hazard ratios for eGFRcr-cys versus mGFR was 1.03, with a 95% confidence interval of 0.96 to 1.10, indicating close concordance.
The single-marker equations were less aligned with the direct measurement. Creatinine-based eGFR underestimated the mortality association, with a ratio of hazard ratios of 0.87 and a 95% confidence interval of 0.79 to 0.95. Cystatin C-based eGFR went in the opposite direction and overestimated risk, with a ratio of hazard ratios of 1.17 and a 95% confidence interval of 1.08 to 1.27. Those differences matter because they show how biomarker choice can shift clinical interpretation at the same nominal level of kidney function.
This pattern is plausible at the bedside. Creatinine is influenced by muscle mass and other nonrenal factors, which can blunt apparent kidney risk in some patients. Cystatin C can be affected by other biological and inflammatory states, which may push risk estimates upward. The combined equation appears to smooth those distortions more effectively, which helps explain why it resembled measured GFR more closely than either biomarker alone.
A single equation cannot fully replace measured GFR when precision is needed. Still, the data support the clinical habit of using the combined creatinine-cystatin C estimate when risk assessment must be as accurate as possible, particularly near decision thresholds.
Why This Cohort Still Supports the 60 Threshold
This study does not overturn current kidney disease definitions; it strengthens them. Adults with an mGFR of 60 mL/min/1.73 m2 had clearly worse survival and a higher chance of kidney failure than those at 90 mL/min/1.73 m2, even after adjustment for age, sex, body mass index, medical history, medications, and urine albumin-to-creatinine ratio. The association remained visible after those standard clinical adjustments, suggesting the signal is not explained away by a handful of obvious confounders.
The design was observational, so causality cannot be assigned. Even so, the scale of the cohort, the direct measurement of GFR with iohexol clearance, and the consistency of the outcome gradient give the findings practical weight. For nephrologists and general clinicians alike, the message is straightforward: when GFR declines to around 60 mL/min/1.73 m2, risk is already elevated enough to be detected in long-term outcomes, not just in laboratory staging systems.
The study also separates two questions that often get blurred together. One question is whether reduced GFR predicts adverse outcomes; the answer here is yes, clearly. The other is which estimating method best mirrors the prognostic information contained in a direct measurement. For mortality, the combined creatinine-cystatin C equation came closest, while creatinine alone lagged and cystatin C alone overshot the measured association.
That distinction has bedside consequences for how clinicians label disease, discuss prognosis, and decide when to intensify monitoring. In patients near the threshold, the choice of estimating equation can influence whether kidney disease appears milder or more severe than it truly is. The direct measurement results in this Swedish cohort argue that the 60 mL/min/1.73 m2 cutoff remains defensible and that combined biomarker estimation is the more reliable surrogate when measured GFR is unavailable.